Zombies and anti-zombies (by guest blogger Keith Frankish)
I'm coming to the end of my stint as guest blogger. It's been fun, and I'd like to thank Eric and everyone who has commented. I thought I'd finish with another post about consciousness.
Every schoolboy knows how the zombie argument goes. Zombies -- physical duplicates of us that lack consciousness –- are clearly conceivable. If a scenario is clearly conceivable, then it is metaphysically possible (the conceivability–possibility, or CP, principle). So zombies are metaphysically possible, and therefore physicalism is false. (Physicalism is the view that consciousness supervenes metaphysically on the physical and thus that there is no world where the physical correlates of consciousness are instantiated without consciousness.) I suspect that the first premise here is false -- that zombies are not conceivable, at least in the rigorous way required by the argument. (For a persuasive statement of the case for this view, see Allin Cottrell's paper, 'Sniffing the Camembert'.) But even if that's wrong, I still don't think the argument works. Like many people, I'm suspicious of the CP principle. And one way to highlight the problem is to note that physicalists can also invoke the principle to argue for their position. Here's how it goes.
Consider anti-zombies. These are beings that are physical duplicates of humans, and that have no non-physical properties, but which are nonetheless conscious. They inhabit an anti-zombie world, which is a physical duplicate of ours, but where no non-physical properties are instantiated. (Physicalists think that we are anti-zombies, of course.) Then we can run an anti-zombie argument for physicalism, as follows. Anti-zombies are conceivable and therefore, by the CP principle, metaphysically possible. And if anti-zombies are metaphysically possible, then physicalism is true. The last step may seem a big one, but it should be uncontroversial. In the anti-zombie world consciousness is physical, so the microphysical features of that world are metaphysically sufficient for consciousness, and any world with the same microphysical features will have the same distribution of phenomenal properties. But, by definition, our world has the same microphysical features as the anti-zombie world. Hence the microphysical features of our world are metaphysically sufficient for the existence of consciousness, which is to say that physicalism is true.
The argument has been anticipated by various writers -- notably Peter Marton -- but I've but tried give it a definitive statement in a recent paper (available here for those with a Blackwell Synergy subscription). As I stress in the paper, the only response available to defenders of the zombie argument is to deny the first premise, that anti-zombies are conceivable.
The point can be made independently by considering the unique world that is a physical duplicate of ours and where no further, non-physical properties are instantiated. This should be a zombie world, if any is. But it's also the only candidate for an anti-zombie world. Thus, the possibility of zombies is incompatible with that of anti-zombies. And if conceivability entails possibility, then the conceivability of zombies is incompatible with that of anti-zombies. So defenders of the zombie argument must deny that anti-zombies are conceivable.
Now of course physicalism is the view that we are anti-zombies, so if anti-zombies aren't conceivable then physicalism isn't conceivable either. In short, if you want to endorse the zombie argument, then you have to maintain that physicalism is inconceivable.
That's all from me. So long and thanks for all the fish.